Hydrothermal zeolite activation

ABSTRACT

The acid activity of a high silica content crystalline zeolite that contains framework boron is increased by hydrolyzing a portion of the boron and compositing the crystals with a binder that contains alumina.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of copending application Ser. No. 725,979 filedon Apr. 22, 1985, now abandoned, which is a continuation-in-part ofapplication Ser. No. 631,689, filed July 16, 1984, now U.S. Pat. No.4,526,880.

FIELD OF THE INVENTION

This invention relates to a method for increasing the catalytic activityof crystalline zeolites. In particular, a novel activation process isprovided to enhance the alpha value of high-silica ZSM-5 type catalystsby hydrothermal treatment in contact with an inorganic activating agent.

BACKGROUND OF THE INVENTION

Zeolite catalysts have become widely used in the processing of petroleumand in the production of various petrochemicals. Reactions such ascracking, hydrocracking, catalytic dewaxing, alkylation, dealkylation,transalkylation, isomerization, polymerization, addition,disproportionation and other acid catalyzed reactions may be performedwith the aid of these catalysts. Both natural and synthetic zeolites areknown to be active for reactions of these kinds.

The common crystalline zeolite catalysts are the aluminosilicates suchas Zeolites A, X, Y and mordenite. Structurally, each such material canbe described as a robust three dimensional framework of SiO₄ and AlO₄tetrahedra that is crosslinked by the sharing of oxygen atoms wherebythe ratio of total aluminum and silicon atoms to oxygen is 1:2. Thesestructures (as well as other crystalline zeolites of catalyticusefulness) are porous, and permit access of reactant molecules to theinterior of the crystal through windows formed of eight-membered rings(small pore) or of twelve-membered rings (large pore). Theelectrovalence of the aluminum that is tetrahedrally contained in therobust framework is balanced by the inclusion of cations in the channels(pores) of the crystal.

An "oxide" empirical formula that has been used to describe the aboveclass of crystalline zeolites is

    M.sub.2/n O.Al.sub.2 O.sub.3.xSiO.sub.2.yH.sub.2 O

wherein M is a cation with valence n, x has a value of from 2 to 10, andy has a value which depends on the pore volume of the particular crystalstructure under discussion. The empirical oxide formula may be rewrittenas a general "structural" formula

    M.sub.2/n (AlO.sub.2.wSiO.sub.2)yH.sub.2 O

wherein M and y are defined as above, and wherein w has a value from 1to 5. In this representation, the composition of the robust framework iscontained within the parentheses, and the material (cations and water)contained in the channels is shown outside the parentheses. One skilledin the art will recognize that "x" in the empirical oxide formularepresents the mole ratio of silica to alumina in the robust frameworkof a crystalline zeolite, and may be referred to herein simply by theexpression in common usage, i.e. "the silica to alumina ratio". Further,the term "framework", whenever used herein, is intended to refer to therobust framework described above. (See "Zeolite Molecular Sieves",Donald W. Breck, Chapter One, John Wiley and Sons, New York, N.Y. 1974,which is incorporated herein by reference as background material).

With few exceptions (such as with Zeolite A wherein x=2), there arefewer alumina tetrahedra than silica tetrahedra in the robust frameworksof the crystalline zeolites. Thus, in general, aluminum represents theminor tetrahedrally coordinated constituent of the robust frameworks ofthe common zeolites found in nature or prepared by the usual syntheticmethods.

For the above common zeolite compositions, wherein x has a value of 2 to10, it is known that the ion exchange capacity measured in conventionalfashion is directly proportional to the amount of the minor constituentin the robust framework, provided that the exchanging cations are not solarge as to be excluded by the pores. If the zeolite is exchanged withammonium ions and calcined to convert it to the hydrogen form, itacquires a large catalytic activity measured by the alpha activity testfor cracking n-hexane, which test is more fully described below. And,the ammonium form of itself desorbs ammonia at high temperature in acharacteristic fashion.

It is generally recognized that the composition of the robust frameworkof the synthetic common zeolites, wherein x=2 to 10, may be variedwithin relatively narrow limits by changing the proportion of reactants,e.g., increasing the concentration of the silica relative to the aluminain the zeolite forming mixture. However, definite limits in the maximumobtainable silica to alumina mole ratio are observed. For example,synthetic faujasites having a silica to alumina mole ratio of about 5.2to 5.6 can be obtained by changing said relative proportions. However,if the silica proportion is increased above the level which produces the5.6 ratio, no commensurate increase in the silica to alumina mole ratioof the crystallized synthetic faujasite is observed. Thus, the silica toalumina mole ratio of about 5.6 must be considered an upper limit forsynthetic faujasite in a preparative process using conventionalreagents. Corresponding upper limits in the silica to alumina mole ratioof mordenite and erionite via the synthetic pathway are also observed.It is sometimes desirable to obtain a particular zeolite, for any ofseveral reasons, with a higher silica to alumina ratio than is availableby direct synthesis. U.S. Pat. No. 4,273,753 to Chang and the referencescontained therein describe several methods for removing some of thealuminum from the framework by the use of aggressive treatments such assteaming, contact with chelating agents, etc., thereby increasing thesilica to alumina ratio of a crystal. However, no generally usefulmethod appears to have been described for increasing the alumina contentof a zeolite crystal. Thus, although it is relatively easy to reversiblyalter the composition of the materials (cations and water) containedwithin the channels of the crystalline zeolites, no generally usefulmethod is known for reversibly altering the content of the minortetrahedrally coordinated constituent in the structure of the robustframework.

Synthetic high silica content crystalline zeolites have been recentlydiscovered wherein x is at least 12, some forms of these having littleor even substantially no aluminum content. It is of interest that thesezeolites appear to have no natural counterparts. These zeolites havemany advantageous properties and characteristics such as a high degreeof structural stability. They are used or have been proposed for use invarious processes including catalytic processes. Materials of this typeare known in the art and include high silica content aluminosilicates,such as ZSM-5 (U.S. Pat. No. 3,702,886), ZSM-11 (U.S. Pat. No.3,709,979), and ZSM-12 (U.S. Pat. No. 3,832,449) to mention a few.Unlike the zeolites described above wherein x=2 to 5, the silica toalumina ratio for at least some of the high silica content zeolites isunbounded, i.e. the ratio may be infinitely large. ZSM-5 is one suchexample wherein the silica to alumina mole ratio is at least 12. U.S.Pat. No. Re. 29,948 to Dwyer et al. discloses a crystallineorganosilicate essentially free of aluminum and exhibiting an X-raydiffraction pattern characteristic of ZSM-5 type aluminosilicates. U.S.Pat. Nos. 4,061,724, 4,073,865 and 4,104,294 describe microporouscrystalline silicas or organosilicates with very low alumina contents.Some of the high silica content zeolites contain framework boron.

Because of the extremely low alumina content of certain high silicacontent zeolites, when such materials are converted to the ammonium formand calcined in the conventional manner to produce the hydrogen form,they are not as catalytically active as their higher alumina contentcounterparts. In copending U.S. patent application Ser. No. 391,212filed June 23, 1982 (now abandoned), a method is described for enhancingthe acid activity of a high silica content crystalline zeolite havingsubstantially no acid activity, by compositing said zeolite with anacidic inorganic oxide under prescribed conditions.

It is an object of the present invention to provide an improved methodfor increasing the acidic catalytic activity of a high silica contentzeolite that contains framework boron. It is a further object of thisinvention to provide a method for substituting aluminum for boroncontained in the robust framework of a high silica content zeolite. Itis a further object of this invention to provide novel catalyticcompositions prepared by the method of this invention.

BRIEF SUMMARY OF THE INVENTION

We have now found that the acidic catalytic activity of a high silicacontent zeolite that has a silica to alumina ratio greater than 100 to1, and that contains framework boron in an amount of at least 0.1 wt %,is advantageously increased by treating the zeolite crystals with waterunder conditions effective to hydrolyze from the crystal about 10% toabout 95% of the boron contained therein, compositing under hydrousconditions said treated zeolite with fine particles of alumina, andcalcination of the composite, all as more fully described hereinbelow.The compositing and treating may be conducted simultaneously.

The technique is particularly advantageous for treating the hydrogenform or the ammonium form of a zeolite that has a silica to alumina moleratio greater than 100 to 1, and that has a boron content of at least0.1 wt %, preferably a content of 0.2 wt % to about 2.5 wt %.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

As has heretofore been stated, the novel process of this invention isconcerned with the treatment of high silica content zeolite thatcontains at least 0.1 wt % of framework boron. The expression "highsilica content" as used herein means a crystalline zeolite structurethat has a silica to alumina ratio greater than 100 to 1 and morepreferably greater than about 500 to 1 up to and including those highlysiliceous materials where the silica to alumina ratio approachesinfinity. This latter group of highly siliceous materials is exemplifiedby U.S. Pat. Nos. 3,941,871, 4,061,724, 4,073,865 and 4,104,294 whereinthe materials are prepared from reaction solutions which involve nodeliberate addition of aluminum. However, trace quantities of aluminumare usually present as impurities in the forming solutions. The silicato alumina mole ratio may be determined by conventional analysis. Theratio represents, as closely as possible, the ratio in the robustframework of the zeolite crystal, and is intended to exclude materialssuch as aluminum in the binder or in another form within the channels ofthe zeolite. The ratio also may be determined by conventional methodssuch as ammonia desorption/TGA (as described in Thermochimica Acta, 3,pages 113-124 1971), which publication is incorporated herein byreference, or by a determination of the ion-exchange capacity for ametal cation such as caesium.

The preferred high silica content zeolite that is to be activated by theprocess of this invention has the crystal structure of a zeolite of the"ZSM-5 type" as evidenced by X-ray diffraction. This type of zeolitefreely sorbs normal hexane, and has a pore size intermediate between thesmall pore zeolites such as Linde A and the large pore zeolites such asLinde X, the pore windows in the crystals being formed of 10-memberedrings. The crystal framework densities of this type zeolite in the dryhydrogen form is not less than 1.6 grams per cubic centimeter. It isalso known that "ZSM-5 type" zeolites exhibit constrained access tosingly methyl-branched paraffins, and that this constrained access canbe measured by cracking a mixture of n-hexane and 3-methylpentane andderiving therefrom a "Constant Index." "ZSM-5 type" zeolites exhibit aConstraint Index of about 1 to 12 provided they have sufficientcatalytic activity or are activated by the method of this invention toimpart such activity. The boron containing "ZSM-5 type" zeolites usefulfor the process of this invention have a crystal structure exemplifiedby ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48. Column 4,line 30 to column 11, line 26 inclusive of U.S. Pat. No. 4,385,195issued May 24, 1983, and the U.S. Patents referred to therein, areincorporated herein by reference for a detailed description includingthe X-ray diffraction patterns of the foregoing "ZSM-5 type" zeolites;for a detailed description of crystal density and method for measuringthis property; for a detailed description of Constraint Index and methodfor measuring this property; and, for matter related to the foregoing.

Methods for preparing high silica content zeolites that containframework boron are known in the art and are not considered part of thepresent invention. The amount of boron contained therein, for example,may be made to vary by incorporating different amounts of borate ion ina zeolite forming solution, as will be more fully illustratedhereinbelow. Prior to activation by the method of this invention, thechosen zeolite may be calcined to remove organic matter. It is thenpreferably converted by ion exchange to the ammonium form by methodsknown to those skilled in the art. Although either the ammonium or thehydrogen form may be activated, the ammonium form is particularlypreferred by the present method. For purposes of the present invention,the zeolite must contain at least about 0.1 wt % boron, although it maycontain from 0.1 wt % to about 2.5 wt %. In general, the greater theboron content, the greater the enhancement of catalytic activity.

In a preferred embodiment of this invention, the hydrogen form of thecrystals are treated with liquid water at a temperature of about 25° C.to 125° C. for about 0.1 hours to 80 hours to induce hydrolysis withsimultaneous removal of boron from the crystals. The ammonium form alsomay be treated, and even the sodium form, to effect hydrolysis, keepingin mind that these will hydrolyze more slowly than the hydrogen form.However, the hydrolysis of these forms will benefit from use of waterwhich is made mildly acidic, thereby converting in situ the ammonium orthe sodium form to the hydrogen form. Saturated steam also may be usedto induce or to speed hydrolysis, with or without subsequent washing toremove boron. In general, the contemplated conditions for the hydrolysisare:

    ______________________________________                                                    Temperature                                                                             Time                                                    ______________________________________                                        broad         15° C.-200° C.                                                              0.05-100 hrs.                                       preferred     25° C.-125° C.                                                              0.1-80 hrs.                                         most preferred                                                                              50° C.-100° C.                                                              0.2-20 hrs.                                         ______________________________________                                    

Also in a preferred embodiment, the treated crystals are compositedunder hydrous conditions with an alumina-containing material to providea composite containing 10 wt % to 90 wt % of said zeolite crystals. Thepreferred binders include aluminas, especially alpha aluminamonohydrate, and a particularly preferred binder consists of high purityalumina hydrosol (PHFsol, obtained from American Cyanamid Co.). Alphaalumina monohydrate preferably is composited with the crystals bymulling these together in the presence of water followed preferably byextrusion, as described in U.S patent application Ser. No. 391,212 filedJune 23, 1982 (now abandoned), which description is here incorporated byreference as if fully set forth.

A further preferred embodiment involves simultaneous compositing andhydrolysis, such as when the water necessarily present duringcompositing under hydrous conditions with an alumina-containing materialacts as the water necessary for the hydrolysis of the treating step.

After completion of the treating and compositing and before use as acatalyst, if there is reason to believe that the crystals may containorganic matter and/or unwanted cations, these may be removed from theextrudate by the usual calcination and/or ammonium exchange steps knownto those skilled in the art.

While not wishing to be bound by theory, it is believed that theeffectiveness of this invention is a result of migration of aluminuminto defect sites provided by hydrolysis of boron. Whereas eitherframework boron, for example, or framework aluminum, would be expectedto be associated with interstitial cations such as hydrogen ions, thoseassociated with boron have a very low or an undetectable catalyticactivity for cracking n-hexane under conditions at which hydrogen ionsassociated with aluminum have a very high activity. As is known in theart, the acid catalytic activity of a zeolite may be measured by its"alpha value," which is the ratio of the rate constant of a test samplein the hydrogen form for cracking normal hexane to the rate constant ofa standard reference catalyst. Thus, an alpha value=1 means that thetest sample and the standard reference have about the same activity. Thealpha test is described in U.S. Pat. No. 3,354,078 and in The Journal ofCatalysis, Vol. IV, pp. 527-529 (August 1965); both of which areincorporated herein by reference.

This invention will now be illustrated by examples which are not to beinterpreted as limiting the scope thereof, said scope being set forth inthe specification including the appended claims. All parts andproportions are by weight unless explicitly stated to be otherwise.

EXAMPLE 1

ZSM-5 zeolite free of boron was synthesized and converted to thehydrogen form as follows:

Tetrapropylammonium bromide, 86.4 g, was dissolved in 160 g of water.The solution was added, with stirring, to 1286 g of silica sol (LudoxLS, 30% SiO₂). Finally, a solution of 40.8 g of sodium hydroxide (98%)in 80 g of water was added. The reaction mixture was heated in a 2-literstirred autoclave at 120° C. Crystallization was complete after 82hours.

The product was separated from the mother liquor by filtration. It waswashed with water until free of bromide, and dried at ambienttemperature. The dried material gave the X-ray diffraction pattern ofZSM-5.

About 60 g of the dried material was sized 10-14 mesh and calcined for 3hours at 538° C. in flowing nitrogen; heating rate was 5° F. (2.8°C.)/min. The nitrogen was then replaced with dry air, and thecalcination was continued until the material was pure white.

The calcined zeolite was ion exchanged three times with 2700 ml of 0.2Nammonium acetate solution at 160° F. for 2 hours each. The product waswashed with water and dried, both at room temperature.

Five grams of the ammonium-exchanged zeolite was converted to thehydrogen form by calcining in air as follows:

4 hours heat-up to 900° F. (482° C.)

4 hours at 900° F. (482° C.) and

4 hours cooling to ambient temperature.

The calcined, hydrogen form of the ZSM-5, free of boron, is referred toin the examples which follow as Sample A.

The composition and properties of the dried sample before and after ionexchange are shown in Tables I and II.

EXAMPLE 2

ZSM-5 zeolite that contained boron was synthesized and converted to thehydrogen form as follows:

Sodium hydroxide (98%), 20 g, was dissolved in 400 g of water. Boricacid, 31.5 g, was added and dissolved. The remaining solution was added,with stirring, to 475 g of silica sol (Ludox LS, 30% SiO₂). Finally, asolution of 31.8 g of tetrapropylammonium bromide in 120 g of water wasadded with stirring. The reaction mixture was heated in a 2-literautoclave at 120° C. with vigorous stirring. Crystallization wascomplete after 86 hours.

The produce was separated from the mother liquor, washed and dried inthe same manner as described in Example 1. The dried material gave theX-ray diffraction pattern of ZSM-5.

About 60 grams of the dried material was sized and calcined, thecalcined material was ammonium exchanged, and five grams of the ammoniumexchanged material was converted to the hydrogen form, all as describedin Example 1.

The calcined, hydrogen form of the boron-containing ZSM-5 is referred toin the examples which follow as Sample B.

The composition and properties of the dried sample before and after ionexchange are shown in Tables I and II.

                  TABLE I                                                         ______________________________________                                        Composition of Dried Samples                                                  Composition          Example 1 Example 2                                      ______________________________________                                        SiO.sub.2, wt. %     83.82     82.88                                          Al.sub.2 O.sub.3, ppm                                                                              595       550                                            B.sub.2 O.sub.3, wt. %                                                                             0         2.00                                           Na.sub.2 O, wt. %    1.48      0.62                                           N, wt. %             0.85      0.76                                           Ash, wt. %           85.7      86.51                                          SiO.sub.2 /Al.sub.2 O.sub.3, Molar                                                                 2395      2560                                           SiO.sub.2 /(Al.sub.2 O.sub.3 + B.sub.2 O.sub.3), molar                                             NA        47.15                                          B.sub.2 O.sub.3 /(Al.sub.2 O.sub.3 + B.sub.2 O.sub.3), molar                                       0         0.982                                          Sorption (after calcination at 538° C.)                                Cyclohexane, 20 Torr 5.3       6.5                                            n-Hexane, 20 Torr    11.4      9.7                                            Water, 12 Torr       5.4       8.7                                            ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Composition after Ion Exchange                                                                  Example 1                                                                             Example 2                                           ______________________________________                                        SiO.sub.2, wt. %    95.7      89.78                                           Al.sub.2 O.sub.3, ppm                                                                             660       615                                             B.sub.2 O.sub.3, wt. %                                                                            0         1.71                                            Na, wt. %           0.01      0.01                                            N, wt. %            0.03      0.67                                            Ash, wt. %          97.5      91.75                                           SiO.sub.2 /Al.sub.2 O.sub.3                                                                       2465      2480                                            SiO.sub.2 /(Al.sub.2 O.sub.3 + B.sub.2 O.sub.3), molar                                            NA        59.5                                            B.sub.2 O.sub.3 /(Al.sub.2 O.sub.3 + B.sub.2 O.sub.3), molar                                      0         0.976                                           ______________________________________                                    

EXAMPLE 3

Sample A from Example 1 was treated with 250 ml of water at 190° F. (88°C.) for 2 hours. The treated sample was filtered, washed with water atroom temperature and dried at 165° C. The dried sample was analyzed andshowed little change in alumina content (830 ppm).

EXAMPLE 4

Sample B from Example 2 was treated as described in Example 3. The driedsample showed no significant change in alumina content (635 ppm).However, the B₂ O₃ content was 0.64 wt. % compared with 1.71 wt. %before treatment, i.e. about 63% of the boron contained in theion-exchanged crystals had been removed.

EXAMPLE 5

The ammonium form of the boron-free ZSM-5 of Example 1 was compositedwith alumina as follows:

Three grams of the zeolite (based on solids) was dispersed in 18.15 g ofPHF alumina hydrosol (8.9% Al₂ O₃) and mixed thoroughly. A mixture of1.5 ml of concentrated ammonium hydroxide and 1.5 ml of water was addedto the slurry with intensive mixing. The obtained mixture was dried at165° C. for 4 hours and then calcined in a covered crucible using thesame temperature program as described in Example 1 for the calcinationof the ammonium form.

The product was tested in the alpha test and found to have an alphavalue of 8.5.

EXAMPLE 6

The ammonium form of the boron-containing ZSM-5 of Example 2 wascomposited under hydrous conditions with alumina as described in Example5. It was found to have an alpha value of 12.1.

EXAMPLE 7

The product from Example 3 was composited as described in Example 5 andfound to have an alpha value of 9.4.

EXAMPLE 8

The product from Example 4 was composited as described in Example 5. Itwas found to have an alpha value of 15.3.

From the foregoing examples, it is seen that the water treatmentillustrated in Example 3 contributes little to the activity of thecomposite if no boron is present, there is an unexpectedly largerincrease when the crystal contains boron which is partially removed bythe treatment.

EXAMPLE 9

A sample of ZSM-11 that contained boron was prepared as follows:

Sodium hydroxide, 3.3 g, 1.5 g of boric acid and 22.8 g oftetrabutylammonium bromide were dissolved in 200 g of water. Silica sol(Ludox LS, 30% SiO₂) was added with stirring, and the mixture was heatedat 140° C. After 91 hours, a well-crystallized material of ZSM-11structure was obtained.

    ______________________________________                                        Sorption capacities, g/100 g:                                                 Cyclohexane, 20 Torr                                                                              2.5                                                       n-Hexane, 20 Torr   12.5                                                      Water, 12 Torr      7.8                                                       Chemical Composition:                                                         SiO.sub.2, wt. %    81.9                                                      Al.sub.2 O.sub.3, ppm                                                                             500                                                       B.sub.2 O.sub.3, wt. %                                                                            1.42                                                      Na.sub.2 O, wt. %   1.08                                                      N, wt. %            0.66                                                      Ash, wt. %          84.8                                                      SiO.sub.2 /(Al.sub.2 O.sub.3 + B.sub.2 O.sub.3)                                                   65.3                                                      B/(Al + B)          0.97                                                      ______________________________________                                    

A portion of the product is calcined and converted to the ammonium formby the procedure described in Example 1.

An aliquot of the ammonium form is treated with a dilute solution ofacetic acid for 6 hours at 200° F., filtered, washed and dried.

Portions of each of the ammonium form and of the water-treated productare composited with alumina and calcined, as described in Example 5.

The composited calcined water-treated product is found to have asubstantially higher alpha value than its ammonium-form counterpartwhich was not subjected to hydrolysis.

What is claimed is:
 1. An improved method for enhancing the catalyticactivity of a composition consisting essentially of crystals of a highsilica content crystalline zeolite that contains from about 0.1 wt % toabout 2.5 wt % of framework boron, said crystals having a silica toalumina mole ratio of at least 100, which method comprisessimultaneously treating and compositing said crystals under hydrousconditions with fine particles of an alumina-containing material wherebyfrom about 10% to about 95% of said boron is hydrolyzed and saidcatalytic activity is increased, and recovering said composited treatedcrystals of enhanced catalytic activity.
 2. The method described inclaim 1 wherein said high silica content crystalline zeolite has aConstraint Index of from 1 to
 12. 3. The method described in claim 2wherein said high silica crystalline zeolite has a silica to aluminaratio greater than about 500 and is selected from the group consistingof ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48.
 4. Themethod described in claim 3 wherein said zeolite is ZSM-5 or ZSM-11. 5.The method described in claim 1 wherein said crystals are converted tothe hydrogen form prior to said simultaneous treating and compositing.6. The method described in claim 2 wherein said crystals are convertedto the hydrogen form prior to said simultaneous treating andcompositing.
 7. The method described in claim 1 wherein said alumina isan aqueous alumina sol or alpha alumina monohydrate.
 8. The methoddescribed in claim 2 wherein said alumina is an aqueous alumina sol oralpha alumina monohydrate.
 9. The method described in claim 5 whereinsaid alumina is an aqueous alumina sol or alpha alumina monohydrate. 10.The method described in claim 6 wherein said alumina is an aqueousalumina sol or alpha alumina monohydrate.
 11. The product produced bythe method of claim
 1. 12. The product produced by the method of claim2.
 13. The product produced by the method of claim
 3. 14. The productproduced by the method of claim
 4. 15. The product produced by themethod of claim
 5. 16. The product produced by the method of claim 6.17. The product produced by the method of claim
 7. 18. The productproduced by the method of claim
 8. 19. The product produced by themethod of claim
 9. 20. The product produced by the method of claim 10.